Membranes, and more particularly, membranes useful for containing fluids, including liquids and/or gases, in a controlled manner, have been employed for years in a wide variety of products ranging from bladders useful in inflatable objects, including vehicle tires and sporting goods for example; to accumulators used on heavy machinery; to cushioning devices useful in footwear. Regardless of the intended use, membranes must generally be flexible, resistant to environmental degradation and exhibit excellent gas transmission controls. Often, however, materials which exhibit acceptable flexibility characteristics tend to have an unacceptably low level of resistance to gas permeation. In contrast, materials which exhibit an acceptable level of resistance to gas permeation tend to have an unacceptably low level of flexibility.
In an attempt to address the concerns of both flexibility and imperviousness to gases, U.S. Pat. No. 5,036,110 which issued Jun. 30, 1991, to Moreaux describes resilient membranes for fitting hydropneumatic accumulators. According to Moreaux '110, the membrane disclosed consists of a film formed from a graft polymer which is the reaction product of an aromatic thermoplastic polyurethane with a copolymer of ethylene and vinyl alcohol, with this film being sandwiched between layers of thermoplastic polyurethane to form a laminate. While Moreaux '110 attempts to address the concerns in the art relating to flexibility and imperviousness to gases, a perceived drawback of Moreaux is that the film described is not processable utilizing conventional techniques such as sheet extrusion, for example. Thus, the present invention is directed to membranes which are flexible, have good resistance to gas transmission, and under certain embodiments are processable into laminates utilizing conventional techniques such as sheet extrusion which are highly resistant to delamination.
While it should be understood by those skilled in the art upon review of the following specification and claims that the membranes of the present invention have a broad range of applications, including but not limited to bladders for inflatable objects such as footballs, basketballs, soccer balls, inner tubes; substantially rigid flotation devices such as boat hulls; flexible floatation devices such as tubes or rafts; as a component of medical equipment such as catheter balloons; fuel lines and fuel storage tanks; various cushioning devices such as those incorporated as part of an article of footwear or clothing; as part of an article of furniture such as chairs and seats, as part of a bicycle or saddle, as part of protective equipment including shin guards and helmets; as a supporting element for articles of furniture and, more particularly, lumbar supports; as part of a prosthetic or orthopedic device; as a portion of a vehicle tire and particularly, the outer layer of the tire, as well as being incorporated as part of certain recreation equipment such as components of wheels for in-line or roller skates, to name a few, still other applications are possible. For example, one highly desirable application for the membranes of the present invention include their use in forming accumulators which are operable under high pressure environments such as hydraulic accumulators as will be discussed in greater detail below.
For convenience, but without limitation, the membranes of the present invention will hereinafter generally be described in terms of either accumulators or in terms of still another highly desirable application, namely for cushioning devices used in footwear. In order to fully discuss the applicability of the membranes in terms of cushioning devices for footwear, a description of footwear in general is believed to be necessary.
Footwear, or more precisely, shoes generally include two major categories of components namely, a shoe upper and the sole. The general purpose of the shoe upper is to snugly and comfortably enclose the foot. Ideally, the shoe upper should be made from an attractive, highly durable, yet comfortable material or combination of materials. The sole, which also can be made from one or more durable materials, is particularly designed to provide traction and protect the wearer's feet and body during use. The considerable forces generated during athletic activities require that the sole of an athletic shoe provide enhanced protection and shock absorption for the feet, ankles and legs of the wearer. For example, impacts which occur during running activities can generate forces of up to 2-3 times the body weight of an individual while certain other activities such as, for example, playing basketball have been known to generate forces of up to approximately 6-10 times an individual's body weight. Accordingly, many shoes and, more particularly, many athletic shoes are now provided with some type of resilient, shock-absorbent material or shock-absorbent components to cushion the user during strenuous athletic activity. Such resilient, shock-absorbent materials or components have now commonly come to be referred to in the shoe manufacturing industry as the midsole.
It has therefore been a focus of the industry to seek midsole designs which achieve an effective impact response in which both adequate shock absorption and resiliency are appropriately taken into account. Such resilient, shock-absorbent materials or components could also be applied to the insole portion of the shoe, which is generally defined as the portion of the shoe upper directly underlining the plantar surface of the foot.
A particular focus in the footwear manufacturing industry has been to seek midsole or insert structure designs which are adapted to contain fluids, in either the liquid or gaseous state, or both. Examples of gas-filled structures which are utilized within the soles of shoes are shown in U.S. Pat. No. 900,867 entitled "Cushion for Footwear" which issued Oct. 13, 1908, to Miller; U.S. Pat. No. 1,069,001 entitled "Cushioned Sole and Heel for Shoes" which issued Jul. 29, 1913, to Guy; U.S. Pat. No. 1,304,915 entitled "Pneumatic Insole" which issued May 27, 1919, to Spinney; U.S. Pat. No. 1,514,468 entitled "Arch Cushion" which issued Nov. 4, 1924, to Schopf; U.S. Pat. No. 2,080,469 entitled "Pneumatic Foot Support" which issued May 18, 1937, to Gilbert; U.S. Pat. No. 2,645,865 entitled "Cushioning Insole for Shoes" which issued Jul. 21, 1953, to Towne; U.S. Pat. No. 2,677,906 entitled "Cushioned Inner Sole for Shoes and Method of Making the Same" which issued May 11, 1954, to Reed; U.S. Pat. No. 4,183,156 entitled "Insole Construction for Articles of Footwear" which issued Jan. 15, 1980, to Rudy; U.S. Pat. No. 4,219,945 entitled "Footwear" which issued Sep. 2, 1980, also to Rudy; U.S. Pat. No. 4,722,131 entitled "Air Cushion Shoe Sole" which issued Feb. 2, 1988, to Huang; and U.S. Pat. No. 4,864,738 entitled "Sole Construction for Footwear" which issued Sep. 12, 1989, to Horovitz. As will be recognized by those skilled in the art, such gas filled structures often referred to in the shoe manufacturing industry as "bladders" typically fall into two broad categories, namely (1) "permanently" inflated systems such as those disclosed in U.S. Pat. Nos. 4,183,156 and 4,219,945 and (2) pump and valve adjustable systems as exemplified by U.S. Pat. No. 4,722,131. By way of further example, athletic shoes of the type disclosed in U.S. Pat. No. 4,182,156 which include "permanently" inflated bladders have been successfully sold under the trade mark "Air-Sole" and other trademarks by Nike, Inc. of Beaverton, Oreg. To date, millions of pairs of athletic shoes of this type have been sold in the United States and throughout the world.
The permanently inflated bladders have historically been constructed under methods using a flexible thermoplastic material which is inflated with a large molecule, low solubility coefficient gas otherwise referred to in the industry as a "super gas." By way of example, U.S. Pat. No. 4,340,626 entitled "Diffusion Pumping Apparatus Self-Inflating Device" which issued Jul. 20, 1982, to Rudy, which is expressly incorporated herein by reference, discloses selectively permeable sheets of film which are formed into a bladder and thereafter inflated with a gas or mixture of gases to a prescribed pressure which preferably is above atmospheric pressure. The gas or gases utilized ideally have a relatively low diffusion rate through the selectively permeable bladder to the exterior environment while gases such as nitrogen, oxygen and argon which are contained in the atmosphere and have a relatively high diffusion rate are able to penetrate the bladder. This produces an increase in the total pressure within the bladder, by the addition of the partial pressures of the nitrogen, oxygen and argon from the atmosphere to the partial pressures of the gas or gases contained initially injected into the bladder upon inflation. This concept of a relative one-way addition of gases to enhance the total pressure of the bladder is now known as "diffusion pumping."
With regard to the systems utilized within the footwear manufacturing industry prior to and shortly after the introduction of the Air-Solen.TM. athletic shoes, many of the midsole bladders consisted of a single layer gas barrier type films made from polyvinylidene chloride based materials such as Saran.RTM. (which is a registered trademark of the Dow Chemical Co.) and which by their nature are rigid plastics, having relatively poor flex fatigue, heat sealability and elasticity.
Still further, bladder films made under techniques such as laminations and coatings which involve one or more barrier materials in combination with a flexible bladder material (such as various thermoplastics) can potentially present a wide variety of problems to solve. Such difficulties with composite constructions include layer separation, peeling, gas diffusion or capillary action at weld interfaces, low elongation which leads to wrinkling of the inflated product, cloudy appearing finished bladders, reduced puncture resistance and tear strength, resistance to formation via blow-molding and/or heat-sealing and RF welding, high cost processing, and difficulty with foam encapsulation and adhesive bonding, among others.
Yet another issue with previously known multi-layer bladders is the use of tie-layers or adhesives in preparing laminates. The use of such tie layers or adhesives generally prevent regrinding and recycling of any waste materials created during product formation back into an usable product, and thus, also contribute to high cost of manufacturing and relative waste. These and other perceived short comings of the prior art are described in more extensive detail in U.S. Pat. Nos. 4,340,626; 4,936,029 and 5,042,176, all of which are hereby expressly incorporated by reference.
Previously known multi-layer bladders which specifically eliminate adhesive tie layers have been known to separate or de-laminate especially along seams and edges. Thus, it has been a relatively recent focus of the industry to develop laminated bladders which reduce or eliminate the occurrence of delamination ideally without the use of a "tie layer." In this regard, the cushioning devices disclosed in co-pending U.S. application patent Ser. Nos. 08/299,286 and 08/299,287 eliminate adhesive tie layers by providing membranes including a first layer of thermoplastic urethane and a second layer including a barrier material such as a copolymer of ethylene and vinyl alcohol wherein hydrogen bonding occurs over a segment of the membranes between the first and second layers. While the membranes disclosed in U.S. patent application Ser. No. 08/299,287 and the laminated flexible membranes of U.S. patent application Ser. No. 08/299,286 are believed to offer a significant improvement in the art, still further improvements are offered according to the teachings of the present invention.
With the extensive commercial success of the products such as the Air-Sole.TM. shoes, consumers have been able to enjoy products with a long service life, superior shock absorbency and resiliency, reasonable cost, and inflation stability, without having to resort to pumps and valves. Thus, in light of the significant commercial acceptance and success that has been achieved through the use of long life inflated gas filled bladders, it is highly desirable to develop advancements relating to such products. One goal then is to provide flexible, "permanently" inflated, gas-filled shoe cushioning components which meet, and hopefully exceed, performance achieved by such products as the Air-Sole.TM. athletic shoes offered by Nike, Inc.
An accepted method of measuring the relative permeance, permeability and diffusion of different film materials is set forth in the procedure designated as ASTM D-1434-82-V. According to ASTM D-1434-82-V, permeance, permeability and diffusion are measured by the following formulas: ##EQU1##
By utilizing the above listed formulas, the gas transmission rate in combination with a constant pressure differential and the film's thickness, can be utilized to define the movement of gas under specific conditions. In this regard, the preferred gas transmission rate (GTR) for a membrane having an average thickness of approximately 20.0 mils such as those useful for forming a cushioning device used as a shoe component which seeks to meet the rigorous demands of fatigue resistance imposed by heavy and repeated impacts will preferably have a gas transmission rate (GTR) of 15.0 or less for nitrogen gas according to ASTM D-1434-82-V. More preferably, the membranes will have a GTR of less than about 2.0 at an average thickness of 20 mils.
It is, therefore, one object of the present invention to provide membranes including both single layer and multi-layer constructions which offer enhanced flexibility, durability and resistance to the undesired transmission of fluids therethrough.
It is another object of the present invention to provide membranes which can be inflated with a gas such as nitrogen wherein the membrane provides for a gas transmission rate value of 15.0 or less, based on a 20 mils average thickness.
It is still another object of the present invention to provide membranes, particularly those employed as cushioning devices, having a relatively high degree of transparency.
It is another object of the present invention to provide monolayer membranes which are readily processable into various products.
It is yet another object of the present invention to provide monolayer membranes and, under certain applications, multi-layer membranes which are reprocessable and repairable.
It is yet another object of the present invention to provide membranes which can be formed into laminated objects such as cushioning devices or accumulators, among others, which better resist delamination and also may not require a tie layer between the layers.
It is a further object of the present invention to provide membranes which are formable utilizing various techniques including, but not limited to, blow-molding, tubing, sheet extrusion, vacuum-forming, heat-sealing, casting, liquid casting, low pressure casting, spin casting, reaction injection molding and RF welding.
Still another object of the present invention is to provide membranes which prevent gas from escaping along interfaces between the layers in laminated embodiments and particularly along seams via capillary action.
It is yet another object of the present invention to provide a membrane which allows for footwear processing such as encapsulation of a membrane within a formable material.
While the aforementioned objects provide guidance as to possible applications and advantages for the membranes of the present invention, it should be recognized by those skilled in the art that the recited objects are not intended to be exhaustive or limiting.